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Third Manufacturing Method's a Charm, Right?

Posted by qwindelzorf on April 9, 2011

Now we're getting close to caught up. The vacuum forming failure occurred in the middle of March and we started on the molds a week later. This post will get us fully caught up so we can just post current events from here on out.

So far, we've tried two methods of making the Portal Sentry and both of them have been abject failures. At this point, we were both a little bit dejected, but we'd already put a lot of time and money into this thing, so we didn't really want to give up. We had one more method that we wanted to try: fiberglass.

Qwindelzorf and I both have some composites experience. We both know exactly how to make the molds and do the layups, but it takes quite a bit of work to get a mold finished well enough to pull a couple parts out of, and we hadn't wanted to go through the process that we both knew was long and boring. At that point, though, it was fiberglass or nothing. I still had enough foam left to do the necessary molds, one for the pod, one for the body, a plug for the eye cutout, and the left and right knee. The back knee is essentially a right knee and a left knee glued together, which is exactly what we're planning on doing to avoid making another mold. Once again, we fired up the CNC mill to cut the slices, except this time we're making female molds so that we get a nice exterior finish.



The molds came out pretty well, and the toolpath was even better than I expected:


Just by sanding the foam, we were able to get a pretty smooth finish:


To fill the voids and give the molds a little more strength, we got some plaster and gave them a nice coat:


The first coat of plaster did wonders for the surface, but when we tried to use more to touch up a couple problem areas, we discovered that the plaster is so hydrophilic that the first layer sucked all the moisture out of the new plaster and made it unworkable almost instantly. To get around this, we used a trick I picked up doing composites in college. Normal household spackle isn't good for building up corners or anything, but it is great for skimming over surfaces to fill small voids and give an amazingly easy to sand surface. With the surface evened up, it was time for the tedious sanding and painting that made us avoid this method in the first place.

For those of you who have never done this before, here's how it works. You start with something relatively smooth (we had sanded the plaster/spackle with 220 grit sandpaper) and give it a coat of spray primer:


Note the white layer already on the mold. We had to brush Kilz onto these molds before spraying primer because the aerosol would attack the foam if we didn't. This made our lives more difficult because we had to sand the brush texture out of the mold, but better than having the molds get eaten. After painting, we sanded the primer with 220 and 320 grit sandpaper, primed it again, sanded with 320 and 400, then gave it a light finish pass with 600 grit sandpaper. On bigger molds where we really needed a smooth part, I've gone all the way up to 800 grit wet sanding, but we decided that 600 dry was enough. That left us with something looking like this:


It doesn't look much, but it's very smooth at this point. Now it's time for the wax. When I ordered the fiberglass for this, I found the mold wax and mold release that I've used before so I picked some up to make our lives easier. After 4 coats of wax, the pod mold is almost ready for a layup:


The pod mold is the only one done at this point as it is probably the easiest one to work on. There is a shot of the body mold further up this post, and as you can see, the internal geometry is more complex, making it a pain to finish, and I'm sure it will be a pain to layup in. It is currently in the middle of the sand/prime/sand/prime cycle. The eye and knee molds have been cut, but not much finish work has happened on them yet. Here they are in their current forms:

IMG_3242 IMG_3243

We should get a lot of this done in the next couple weeks and hopefully will have some pieces to show. We were hoping to have the whole thing done by the release of Portal 2, but with the setbacks that we've had, that's not going to happen. It'll be done when it's done. We have ideas for all the mechanical and electrical systems, so that part of it should go pretty quickly once we have a shell.